1. Technical Field
The invention relates to a process for drilling into a subterranean hydrocarbon-bearing formation and more particularly to a process for minimizing lost circulation of a drilling fluid when drilling into a subterranean hydrocarbon-bearing formation.
2. Background Information
A drilling fluid is a fluid which is circulated from an earthen surface down through a drilled out wellbore to a drilling face and back to the surface when drilling into a subterranean formation which contains hydrocarbons. Drilling fluids are specifically designed to perform a number of functions, including cooling and lubricating the drill bit, removing drill cuttings from the wellbore, supporting the weight of the drill pipe and drill bit, providing a hydrostatic head to maintain the integrity of the wellbore walls, preventing significant flow of fluids across the wellbore face into the wellbore and vice versa. The most common conventional drilling fluids known in the art are termed "drilling muds", which are dispersions of solid particles in a liquid. Examples of drilling muds are aqueous dispersions of clays (e.g. bentonite) and/or gypsum.
A common problem encountered during drilling operations is "lost circulation", which is the excessive flow of drilling fluids out of the wellbore. The drilling fluids are either lost to the formation matrix or to voids in direct communication with the wellbore. Lost circulation is undesirable from an economic standpoint because it requires one to continually replenish the wellbore with costly drilling fluid. Lost circulation is also undesirable from an operational and safety standpoint because it can damage the pay zone and in extreme cases it can result in a blowout of the hydrocarbon zone followed by a well fire.
Drilling fluids are typically formulated to contain one or more viscosifiers, such as polymeric additives, in an effort to control lost circulation. See, for example U.S. Pat. No. 4,740,319 to Patel et al, 4,726,906 to Chen et al, U.S. Pat. No. 4,675,119 to Farrar et al and U.S. Pat. No. 4,282,928 to McDonald et al. Materials which inhibit the flow of drilling fluids from the wellbore into the formation, are termed "lost circulation fluids".
Unfortunately many lost circulation fluids known in the art are unsatisfactory because of operational limitations restricting their utility. For example, some lost circulation fluids are ineffective in the presence of high salt concentration brines. Others undergo thermal degradation when subjected to high operational temperatures. The most significant shortcoming of lost circulation fluids is their inability to effectively control lost circulation encountered when drilling through voids occurring in the formation.
Thus, a need exists for a lost circulation treatment using a material which effectively prevents or reduces lost circulation of drilling fluids, particularly in cases where lost circulation fluids are ineffective. Further, a need exists for a lost circulation treatment which has sufficient strength and integrity to minimize lost circulation into voids in direct communication with the wellbore, such as fractures, fracture networks, vugs, washouts, cavities, and the like.